import InstalledGames
import AddGameScreen
import BasisKlasse

use_tray = True
try:
	import TrayIcon
except ImportError:
	use_tray = False
import os
import LoginScreen

import pygtk
pygtk.require("2.0") # Minimaal versie 2
import gtk 

## Main class, this function holds most other classes related to the interface
class MainWidget(BasisKlasse.Base):
	## xml file from which the menu is loaded
	MENU_XML = os.path.join(os.path.dirname(__file__), "res/menu.xml") ## <=== this is the line that is causing the problem.

Trace back:

Traceback (most recent call last):
  File "E:\Programming\stoombootje\StoomBoot\src\client\MainWidget.py", line 18, in <module>
    class MainWidget(BasisKlasse.Base):
  File "E:\Programming\stoombootje\StoomBoot\src\client\MainWidget.py", line 20, in MainWidget
    MENU_XML = os.path.join(os.path.dirname(__file__), "res/menu.xml")
NameError: name '__file__' is not defined